Field of the Invention
The present invention elates to a method of manufacturing hexagonal ferrite powder, hexagonal ferrite powder, a magnetic recording medium and a method of manufacturing a magnetic recording medium.
Discussion of the Background
Hexagonal ferrite powder is widely employed as the ferromagnetic powder contained in the magnetic layer of magnetic recording media. The coercive force thereof is great enough for use in permanent magnetic materials. The magnetic anisotropy that is the basis of the coercive force derives from its crystal structure. Thus, high coercive force can be maintained even when the size of the particles is reduced. In magnetic recording media having a magnetic layer employing hexagonal ferrite powder, the high-density characteristic can be good due to the vertical component. Thus, hexagonal ferrite powder is ferromagnetic powder that is suited to achieving higher density recording.
Various methods are employed to manufacture hexagonal ferrite powder, such as the coprecipitation method and the glass crystallization method. A manufacturing method (referred to hereinafter as the hydrothermal synthesis process) that utilizes a hydrothermal synthesis reaction in the presence of heated and pressurized water known as supercritical water or subcritical water has also been proposed (for example, see WO 2015/046496A1 and Japanese Unexamined Patent Publication (KOKAI) No. 2009-208969, which are expressly incorporated herein by reference in their entirety).